Set process name in ps output to make operations safer.

This commit allows Redis to set a process name that includes the binding
address and the port number in order to make operations simpler.

Redis children processes doing AOF rewrites or RDB saving change the
name into redis-aof-rewrite and redis-rdb-bgsave respectively.

This in general makes harder to kill the wrong process because of an
error and makes simpler to identify saving children.

This feature was suggested by Arnaud GRANAL in the Redis Google Group,
Arnaud also pointed me to the setproctitle.c implementation includeed in
this commit.

This feature should work on all the Linux, OSX, and all the three major
BSD systems.

src/config.h

@@ -105,6 +105,18 @@
 #define rdb_fsync_range(fd,off,size) fsync(fd)
 #endif
 
+/* Check if we can use setproctitle().
+ * BSD systems have support for it, we provide an implementation for
+ * Linux and osx. */
+#if (defined __NetBSD__ || defined __FreeBSD__ || defined __OpenBSD__)
+#define USE_SETPROCTITLE
+#endif
+
+#if (defined __linux || defined __APPLE__)
+#define USE_SETPROCTITLE
+void setproctitle(const char *fmt, ...);
+#endif
+
 /* Byte ordering detection */
 #include <sys/types.h> /* This will likely define BYTE_ORDER */